(1) Field of the Invention
This invention relates generally to charge pumps and relates more specifically to charge pumps being capable to operate from one of multiple power supplies wherein each supply is able to vary over a range of voltages and where any one supply can be of a higher or lower voltage than the others.
(2) Description of the Prior Art
Electronic displays (e.g. LCDs, electrophoretic displays, etc.) generally require voltage multipliers such as e.g. charge pumps to operate. Where multiple power sources are available (e.g. mains, battery), which have different voltage outputs, reconfiguration of the charge pump has to be undertaken to:
a) maintain the output voltage for correct operation of the display and its driver
b) prevent damage to components connected to the charge pump and
c) prevent damage to the charge pump itself.
Examples for such different power sources could be a battery, terminal contacts, or terminal coils. It is a challenge for the designer of DC-to DC converters such as charge pumps providing the operation voltage of display drivers to achieve circuits and methods to enable a correct operation with one of two or more power supplies, where each of the power supplies is able to vary over a range of voltages and where any one supply can be of a higher or lower voltage than any of the others.
There are known patents or patent publications dealing with adjusting charge pumps to external voltage sources:
U.S. Patent (U.S. Pat. Nos. 6,370,075 and 6,760,262 to Haeberli et al) disclose an integrated circuit detecting the voltage level of a supply voltage to an integrated circuit. Circuitry on the integrated circuit including a charge pump circuitry adjusts to operate more effectively or efficiently at the voltage level of the supply voltage.
Furthermore there are known patents or patent publications dealing with charge pumps for display drivers:
U.S. Patent (U.S. Pat. No. 7,156,313 to Ou et al.) proposes an IC card with a display panel but without batteries including a contact/contactless communication interface, a microprocessor, an EEPROM, a rectifier/voltage regulator, a display driver, a charge-pump disposed therein, and a display panel disposed thereon. The microprocessor receives the external data, and displays the data on the display panel so that users can look up the external data. The display panel exhibits a double steady-state function having the characteristic that once the data are displayed, no persistent power supply for the display panel is needed, and thus the displayed data will be preserved persistently until the next time the data are updated. In this way, users are not required to use batteries and can avoid being disturbed by the service life of the batteries.
U.S. Patent (U.S. Pat. No. 6,801,077 to Negoi) discloses a charge pump device and a display driver with a charge pump device. Further it discloses to a display module with a display driver using a charge pump device and a telecom terminal having such a display module. To provide a device which needs a charge pump for generating a higher voltage as the supply voltage a charge pump device is proposed containing at least two stages, whereby a stage (S) comprises a switch and a charge device which are arranged to generate a voltage higher than the supply voltage, whereby the stages are arranged in series and a required multiplication factor of the charge pump is adjustable by activating/deactivating a definable number of stages, whereby the switches of each stage are arranged in the same way. Thereby it will achieved a freely programmable multiplication factor of the supply voltage and in the same time having switches in the charge pump which are optimized in the power consumption by programming a multiplication factor smaller than the maximum multiplication factor.
U.S. Patent (U.S. Pat. No. 7,190,359 to Yoneyama) discloses a display driver, an electro-optical device, and a display driving method that can regulate output voltages with high precision and without reducing reliability. The display driver includes an electronic volume value generating circuit that generates an electronic volume value for regulating output voltages, a power supply circuit that generates output voltages using a standard voltage amended based on the electronic volume value, a driving circuit that drives the electro-optical element based on the output voltages corresponding to display data, and an absolute value setting register for setting an electronic volume absolute value. The driving circuit uses an amendment value corresponding to a difference between a given characteristic value set in accordance with the electro-optical element being driven and a center value of a range that can be taken by the electronic volume value to amend the electronic volume absolute value, thereby generating the electronic volume value.